It is well-known that a spectacle case H as shown in FIG. 15(a) is produced by a metal mold using two materials. The spectacle case H is composed of a substantially boat-shaped main body H1 for storing glasses or the like and a lid H2 that is rotatably connected to the main body H1 with hinge portions J. As shown in FIG. 15(b), the hinge portions J are so constructed that an insertion hole b formed in the main body H1 supports an insertion portion (hinge pin) p formed on the lid H2.
The aforementioned spectacle case H is produced using a metal mold with a movable sleeve S. Specifically, the main body H1 and the lid H2 shown in FIG. 15(b) are produced by injecting heat-melted plastic resin into two cavity portions made in the shapes of the main body H1 and the lid H2 under pressure and then cooling the resin. In this specification, the term “cavity portion” indicates a hollow portion in the formed in a closed metal mold as a cavity or a hollow portion formed between a cavity and a core.
In the aforementioned production process, the two cavity portions are connected at the positions corresponding to the insertion holes b and the insertion portions p in the hinge portions J. The movable sleeve S acts as a core for partitioning the heat melted plastic resin between the two cavity portions and providing the shape of the insertion hole b. After the plastic resin is cooled, when the movable sleeve S is detached from the insertion hole b and the insertion portion p as shown in the drawing, a space is formed between the insertion hole b and the insertion portion p.
In the case of molding a precision component, a play between the insertion hole b and the insertion portion p needs to be minimized. However, an extremely thin movable sleeve S reduces the strength of the sleeve itself. For this reason, it has been difficult to narrow the space between the insertion hole b and the insertion portion p in accordance with high precision requirements.
Further, when a collar or the like is provided to an edge e of the insertion portion p so as to prevent the insertion portion from coming off the insertion hole, the spectacle case H is released from the metal mold and then, the collar or the like, which is a separate component from the insertion portion p, must be fixed to the edge e of the insertion portion p in a later process. In other words, it is not possible to produce a collar or the like having a longer diameter than the outer diameter of the insertion portion p on the edge e of the insertion portion p at the same time when the spectacle case H is molded.
Accordingly, in order to solve the above problems, we have eventually found the present invention. An object of the present invention is to provide a metal mold of a simple structure that can be used for producing a combined product and a method of molding such combined product.